Method of producing spheroidal graphite cast iron

ABSTRACT

A method of producing spheroidal graphite cast iron in which the molten cast iron is passed over a nodularizing agent contained in a shallow depression in the bottom of a relatively wide, shallow flow channel. The nodularizing agent is dissolved at the interface between the molten cast iron and nodularizing agent, and the molten cast iron is passed over the nodularizing agent at a rate sufficient to scrub away the minor quantity of vapor produced so that the contact between the solid nodularizing agent and molten cast iron is not interrupted.

United States Patent [191 Lee [451 Mar. 11, 1975 METHOD OF PRODUCING SPHEROIDAL GRAPHITE CAST IRON [75] Inventor: Robert Stormo Lee, Geneseo, Ill.

[73] Assignee: Deere & Company, Moline, Ill.

[22] Filed: Mar. 5, 1973 21 Appl. No.: 338,140

3,765,876 l0/l973 Moore 75/130 R Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Peter D. Rosenberg [57] ABSTRACT A method of producing spheroidal graphite cast iron in which the molten cast iron is passed over a nodularizing agent contained in a shallow depression in the [52] US. Cl. 75/130 R, 75/130 B bottom of a relatively wide Shallow flow Channel. The [51] Int. Cl. C22c 37/04 [58] Field of Search 75/130 R 130 B nodularizing agent 15 dissolved at the interface be tween the molten cast iron and nodularizing agent,

and the molten cast iron is passed over the nodulariz- [56] References cued ing agent at a rate sufficient to scrub away the minor UNITED STATES PATENTS quantity of vapor produced so that the contact be- 3,3ll,469 3/1967 Loper 75/130 R tween the solid nodularizing agent and molten cast 3,492,] Mickelson. R iron is not interrupted 3,498,361 3/1970 Hall 75/130 R 3,703,922 ll/l972 Dunks 75/130 R 8 Claims, 2 Drawing Figures I 2 {/30 I //--'|O 1 CT]? ,[4 I I I IS/i I I, I 1 I I //3 1 METHOD OF PRODUCING SPHEROIDAL GRAPHITE CAST IRON BACKGROUND OF THE INVENTION The present invention relates generally to the production of spheroidal graphite cast iron, and more particularly relates to a method of treating a molten cast iron of such composition as to freeze with free graphite in flake form with a nodularizing agent to convert the graphite to a spheroidal form. I

Most of the commonly employed methods of producing spheroidal graphite cast iron depend upon the use of nodularizing alloys such as magnesium, calcium, lithium, strontium, barium, cerium, didynium, lanthanum, and yttrium which are extremely volatile at the temperature of molten cast iron and therefore present problems in smoke and fume emission, splashing of iron, and variable and low recovery of the nodularizing agent. All of these problems result in increased cost in the production of spheroidal graphite cast iron and some result in poor quality castings. The smoke and fume emissions require large expenditures for pollution control equipment to remove the impurities from the air before it leaves a foundry and also require continued expenditures in disposing of the impurities removed from the air.

The low rate of recovery and variable rate of recovery of the nodularizing agents require the use of excess amounts of the nodularizing agents which are extremelyexpensive. This not only increases the cost, but may result in low-quality castings because of the increase in residual quantities of carrier alloys and the formation of oxides and silicates which become entrapped in the melt to produce dirty castings or dross effects.

A recent improvement in the production of spheroidal graphite cast iron proposes the treatment of the molten cast iron within the mold. This process is fully described in U.S. Pat. No. 3,703,922 which issued to Dunks, et al., on Nov. 28, 1972. According to the process described in the patent, eachmold is provided with a nodularizing agent-containing chamber through which the molten cast iron must pass before entering the mold cavity and the flow of metal through the intermediate chamber is regulated to ensure sufficient time of the molten metal in the intermediate chamber to obtain complete nodularization of the graphite. This process, which is often referred to as inmold nodularization or treatment, eliminates many of the problems previously encountered, but due to the turbulent flow conditions in the chamber the nodularizing agent tends to dissolve nonuniformly and a significant amount of dross which can cause dirty castings is usually formed. In order to reduce dross the inmold nodularization process generally requires preliminary desulphurization of the molten iron. Castings produced according to the inmold process also require special inspection techniques such as ultrasonic inspection and destructive sampling.

SUMMARY OF THE INVENTION The principal object of the present invention is to provide a method for the manufacture of spheroidal graphite cast iron which reduces the smoke and fume emissions normally present in the nodularization of molten cast iron, which greatly increases the recovery of the nodularizing agent, which provides a substantially constant rate of recovery of the nodularizing agent, and which does not require preliminary desulpurization of the molten cast iron or require any special inspection techniques for castings produced according to the method.

A more specific object of the present invention is to provide a method for the production of spheroidal graphite cast iron by which a smoke-free nonviolent nodularizing treatment can be effected using any of the conventional nodularizing alloys, including highmagnesium alloys or elemental magnesium itself, which provides nearly complete recovery of the nodularizing agent, and which method is simple and easily effected with conventional foundry equipment and material handling techniques.

According to the present invention, the nodularizing alloy must be contacted by molten iron and any vapor produced must be scrubbed away from the nodularizing agent so as to not interrupt contact between the nodularizing agent and the molten iron. Air is excluded from the system so that the vapor which is scrubbed away from the nodularizing agent is dissolved in the molten cast iron in a relatively short time. Ithas been found that a practical way to accomplish the method according to the present invention is to flow a relatively wide shallow enclosed laminar stream of iron over a quantity of the nodularizing agent placed in a shallow depression in the bottom of the flow channel.

As will become more apparent hereinafter, the various advantages of the method according to the present invention include a no-smoke, nonviolent treatment, almost complete recovery of the nodularizing agent, and use of conventional inspection techniques for castings produced according to the invention.

The above and additional objects and advantages of the present invention will become apparent to those skilled in the art from a reading of the following de tailed description when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a sectional view of a pouring block providing a flow channel to be used in the method according to the present invention; and

FIG. 2 is a view similar to FIG. 1 but illustrating a slightly modified form of flow block.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order .to carry out the method according to the present invention, it is necessary to provide a flow channel through which the molten cast iron can travel to pass over a nodularizing agent. As illustrated in FIG. 1, the flow channel is formed in a pouring block 10 made of a suitable refractory material. A down sprue 12 provided in the pouring block 10 leads to the entrance of the flow channel 14. The exit end of the flow channel 14 is curved slightly upwardly as at 16 so that when molten iron is poured into the down sprue I2 and passes through the flow channel 14, it must travel up a slight embankment before exiting from the channel. This ensures that the channel 14 will be completely filled when iron is poured through the block 10. A shallow depression or pocket 18 is provided in the bottom of the flow channel 14 and is adapted to receive a nodularizing agent. In FIG. 1, the depression 18 is formed with a smooth arcuate surface so as not to disrupt the substantially laminar flow of the molten metal and cause turbulence in the flow of molten metal through the channel 14. The depression extends across the entire width of the channel and is sized to contain a sufficient amount of nodularizing agent to completely treat the batch of molten iron to be poured through the block.

According to the method of the invention, the depression or pocket 18 is filled with a nodularizing agent of a quantity calculated in a conventional manner to convert the graphite to spheroidal form. The nodulariz-' ing agent can be crushed or a solid block, and can be in an elemental state or an alloy. Molten cast iron of a composition as to freeze with free graphite in flake form is then poured into the down sprue 12 and allowed to flow through the channel 14. The treated molten iron exiting from the channel is collected in any suitable container such as a transfer ladle or pouring ladle. The iron passing through the channel 14 contacts the nodularizing agent in the depression 18 to dissolve the same. As the molten cast iron contacts the nodularizing agent, a minor quantity of vapor is produced, but the movement of the metal scrubs away this vapor so that the interface or direct contact between the molten cast iron and nodularizing agent is not interrupted. Also, since the channel 14 is filled during the pouring process, air is excluded from the system so that the vapor is completely dissolved in the molten iron before exiting from the channel 14.

The following examples will serve to illustrate the invention Example 1: A pouring block similar to that illustrated in FIG. 1 was constructed to have a channel which was 2 inches wide and three-fourths inch deep. Two pounds of crushed 15% magnesium 80% nickel alloy was placed in the depression or pocket 18. Six hundred pounds of base iron at- 2,600 F. and of such composition -as to freeze with free graphite in flake form, containing no magnesium and'with sulphur at 0.03%, was poured through the channel at the rate of ten pounds per second, or at a stream velocity approximately 26.7 inches per second. A microsample taken from the exit stream 2 seconds after the start of pour was found to have spheroidal graphite. A specimen was cut from a solidified slab of the treated cast iron and found to have spheroidal graphite with 0.04% retained magnesium. Retained magnesium plus sulphur reduction was 100% of added magnesium.

During the pouring, the reaction at the depression or pocket 18 was photographed through refractory glass and was observed to be quiet and steady with low vapor emission. The depression inthe channel was located approximately 8 inches from the exit of the channel and this distance appeared to provide sufficient time for nearly complete dissolution of the vapor prior to exit from the channel and exposure to air.

Example 2: In another trial, a crushed 15% magnesium-nickel alloy was placed in the depression of a flow channel having the same dimensions as the channel in Example 1. Base iron at 2,540F. was passed through the pouring block at a stream velocity of 13 inches per second. Samples taken from the exit stream showed spheroidal graphite and contained respectively 0.063% magnesium with 0.33% nickel, and 0.063% magnesium with 0.031% nickel.

Example 3: In a third trial, a crushed 8% magnesiumferrosilicon alloy was placed in the depression of a channel having the same dimensions as the channel in Example 1. Base iron at 2,600 F. was poured through the channel at a stream velocity of 26.7 inches per second. Microsamples taken from the exit stream showed spheroidal graphite.

Example 4: In another trial, a crushed 15% magnesium alloy was placed in the depression in a channel which was 4 inches wide and 1% inches deep. Seventeen hundred pounds of base iron was passed through the pouring block at a stream velocity of approximately 15 inches per second and was collected in a ladle. The composition of the untreated base iron was: carbon 3.76%; silicon 1.98%, manganese 0.49% and sulphur 0.03%. Samples of the treated iron taken from the collection ladle showed spheroidal graphite with 0.057% retained magnesium.

During all four of the above examples, there was no observable smoke or violence associated with the treatment.

From the above examples, it can be seen that to practice the method according to the present invention it is necessary to pass the molten cast iron through a relatively wide shallow channel so that there is sufficient surface contact between the molten iron and the nodularizing agent in the depression to obtain dissolution, and it is necessary to pass the molten iron through the channel at a sufficient rate to scrub away the minor quantities of vapor produced so that the interface between the molten iron and nodularizing agent is not interrupted.

The treatment of the molten cast iron with the nodularizing agent according to the present invention can take place at any place between the melting furnace and final mold. For example, the molten iron can be treated as it is transferred from the melt furnace to a holding furnace, or it can be treated as it is transferred from the holding furnace to a transfer ladle, or it can be treatedas it is transferred from the transfer ladle to a pouring ladle. It is also possible to treat the molten iron as it is transferred from the pouring ladle to the mold, but it is preferable to hold the iron a short time aftertreatment to allow it to clarify by the settling out of nonstandard materials.

Although the depression or pocket 18 in the preferred pouring block illustrated in FIG. 1 is of arcuate cross section in the direction of fluid flow, this configuration is not extremely critical since satisfactory results have been obtained with depressions or pockets of other shapes as long as the shape does not disrupt the substantially laminar flow. For example, FIG. 2 is an illustration of a pouring block having a depression or pocket of shallow V-shape and a pouring block of this configuration has been used successfully. In FIG. 2, the pouring block indicated generally at 20, includes a down sprue 22 which leads to the entrance of a relatively wide shallow channel 24. The exit end of the channel is angled upwardly as at 26 to keep the channel full as molten cast iron is passed therethrough. A shallow V-shaped depression or pocket 28 is provided in the bottom of the channel 24. The slope of the V- shaped pocket cannot be too great or the molten iron will not be able to follow the contour of the nodularizing agent as it is dissolved, and too great a slope could cause turbulence in the stream.

Having thus described the preferred method of the invention, various modifications in the method of the invention will become apparent to those skilled in the art.

I claim:

1. A method of treating molten cast iron for the production of spheroidal graphite cast iron comprising passing molten cast iron of such composition as to freeze with free graphite in flake form through a channel having a width greater than its height and which includes a shallow depression in the lower surface thereof, a nodularizing agent being present in the depression in an amount sufficient to convert the graphite to spheroidal form, said molten cast iron passing through the channel with a substantially laminar flow and contacting said nodularizing agent as it passes through the channel and when passing through the channel traveling at a rate sufficient to scrub away any vapor which forms at the interface between the molten cast iron and the nodularizing agent.

2. A method of treating molten cast iron of such composition as to freeze with free graphite in flake form to convert the free graphite to spheroidal form including the steps of:

a. providing a channel with a shallow pocket formed in the lower surface thereof;

b. filling the pocket with a nodularizing agent in an amount sufficient to convert the graphite in the molten cast iron to be treated to spheroidal form;

0. passing the molten cast iron through the channel with a substantially laminar flow and at a rate sufficient to scrub away any vapor which forms at the interface between the molten cast iron and the nodularizing agent.

3. A method as set forth in claim 2 wherein the pocket is formed in the channel in a position remote from the exit end of the channel to provide time for the dissolution of the scrubbed away vapor prior to exit from the channel.

4. A method as set forth in claim 2 wherein the pocket extends over the entire width of the channel and is formed with a substantially constant cross section transverse to the direction of flow of the molten cast iron.

5. A method as set forth in claim 4 wherein the pocket is formed with an arcuate cross section as viewed in section.

6. A method of producing spheroidal graphite cast iron castings from molten cast iron of such composition as to freeze with free graphite in flake form including the steps of:

a. providing a channel having a width greater than its height and a shallow pocket formed in the lower surface thereof;

b. filling the pocket with a treatment material containing a nodularizing agent in an amount sufficient to convert the graphite in the molten cast iron to spheroidal form;

c. passing the molten cast iron through the channel with a substantially laminar flow and at a rate sufficient to scrub away any vapor which forms at the interface between the molten cast iron and the treatment material; I

d. collecting the molten cast iron as it exits from the channel and holding the same a sufficient time to permit clarification of the molten cast iron; and

e. pouring the molten cast iron into preformed molds.

7. A method of producing an alloy from a batch of molten base metal and an alloying material including the steps of:

- a. providing an enclosed channel having a width greater than its height, open entry and exit ends and a shallow pocket formed in the lower surface thereof spaced from the exit end and extending across the entire width of the channel;

b. filling the pocket with an alloying material in an amount calculated to treat the batch of molten base metal to the extent desired; and

c. passing the molten base metal through the channel with a substantially laminar flow so that it travels over the shallow pocket and contacts and dissolves the alloying material prior to exiting from the channel.

8. A method of producing a magnesium alloy from a batch ofmolten base metal and a magnesium treatment material including the steps of:

a. providing an enclosed channel having a width greater than its height, open entry and exit ends and a shallow pocket formed in the lower surface thereof spaced from the exit end and extending across the entire width of the channel;

b. filling the pocket with a magnesium treatment material in an amount calculated to treat the batch of molten base metal to the extent desired; and

c. passing the molten base metal through the channel with a substantially laminar flow and at a rate sufficient to scrub away any vapor which forms at the interface between the molten base metal and the magnesium treatment material. 

1. A METHOD OF TREATING MOLTEN CAST FOR THE PRODUCTION OF SPHEROIDAL GRAPHITE CAST IRON COMPRISING PASSING MOLTEN CAST IRON OF SUCH COMPOSITION AS TO FREEZE WITH FREE GRAPHITE IN FLAKE FORM THROUGH A CHANNEL HAVING A WIDTH GREATER THAN ITS HEIGHT AND WHICH INCLUDES A SHALLOW DEPRESSION IN THE LOWER SURFACE THEREOF, A NODULARIZING AGENT BEING PRESENT IN THE DEPRESSION IN AN AMOUNT SUFFICIENT TO CONVERT THE GRAPHITE TO SPHEROIDAL FORM, SAID MOLTEN CAST IRON PASSING THROUGH THE CHANNEL WITH A SUBSTANTIALLY LAMINAR FLOW AND CONTACTING NODULARIZING GENT AS IT PASSES THROUGH THE CHANNEL AND WHEN PASSING THROUGH THE CHANNEL TRAVELLING AT A RATE SUFFICIENT TO SCRUB AWAY ANY VAPOR WHICH FORMS AT THE INTERFACE BETWEEN THE MOLTEN CAST IRON AND THE NODULARIZONG AGENT.
 1. A method of treating molten cast iron for the production of spheroidal graphite cast iron comprising passing molten cast iron of such composition as to freeze with free graphite in flake form through a channel having a width greater than its height and which includes a shallow depression in the lower surface thereof, a nodularizing agent being present in the depression in an amount sufficient to convert the graphite to spheroidal form, said molten cast iron passing through the channel with a substantially laminar flow and contacting said nodularizing agent as it passes through the channel and when passing through the channel traveling at a rate sufficient to scrub away any vapor which forms at the interface between the molten cast iron and the nodularizing agent.
 2. A method of treating molten cast iron of such composition as to freeze with free graphite in flake form to convert the free graphite to spheroidal form including the steps of: a. providing a channel with a shallow pocket formed in the lower surface thereof; b. filling the pocket with a nodularizing agent in an amount sufficient to convert the graphite in the molten cast iron to be treated to spheroidal form; c. passing the molten cast iron through the channel with a substantially laminar flow and at a rate sufficient to scrub away any vapor which forms at the interface between the molten cast iron and the nodularizing agent.
 3. A method as set forth in claim 2 wherein the pocket is formed in the channel in a position remote from the exit end of the channel to provide time for the dissolution of the scrubbed away vapor prior to exit from the channel.
 4. A method as set forth in claim 2 wherein the pocket extends over the entire width of the channel and is formed with a substantially constant cross section transverse to the direction of flow of the molten cast iron.
 5. A method as set forth in claim 4 wherein the pocket is formed with an arcuate cross section as viewed in section.
 6. A method of producing spheroidal graphite cast iron castings from molten cast iron of such composition as to freeze with free graphite in flake form including the steps of: a. providing a channel having a width greater than its height and a shallow pocket formed in the lower surface thereof; b. filling the pocket with a treatment material containing a nodularizing agent in an amount sufficient to convert the graphite in the molten cast iron to spheroidal form; c. passing the molten cast iron through the channel with a substantially laminar flow and at a rate sufficient to scrub away any vapor which forms at the interface between the molten cast iron and the treatment material; d. collecting the molten cast iron as it exits from the channel and holding the same a sufficient time to permit clarification of the molten cast iron; and e. pouring the molten cast iron into preformed molds.
 7. A method of producing an alloy from a batch of molten base metal and an alloying material including the steps of: a. providing an enclosed channel having a width greater than its height, open entry and exit ends and a shallow pocket formed in the lower surface thereof spaced from the exit end and extending across the entire width of the channel; b. filling the pocket with an alloying material in an amount calculated to treat the batch of molten base metal to the extent desired; and c. passing the molten base metal through the channel with a substantially laminar flow so that it travels over the shallow pocket and contacts and dissolves the alloying material prior to exiting from the channel. 